Hydraulic vehicle servo-steering arrangements are generally known. In principle, they are based on the fact that the rotation between an input shaft, which is coupled with the steering wheel, and an output shaft, which is part of a servo-steering valve, is converted into a hydraulic current, which in turn is converted into a steering support force. In a generally usual construction, two valve sleeves are used, one of which is securely connected with the input shaft and the other with the output shaft. When the input shaft is rotated relative to the output shaft, the two valve sleeves are also rotated relative to each other. Through this rotation, the hydraulic current is generated, which is then converted into the steering support force, for example in a hydraulic cylinder.
In modern motor vehicles, electronic stability programs are being increasingly used, by means of which the vehicle stability it to be actively improved. A possibility for the action of such an electronic stability program consists in actively engaging in the steering of the vehicle. For example, a correction angle can be superimposed on the steering angle which is given by the driver via the steering wheel. For this purpose, a gearing can be used, which is interposed into the path of the flux of force between the steering wheel and the steerable vehicle wheels. The problem with such a construction consists in ensuring that the vehicle also remains steerable in the case of a possible defect of the gearing.